Enrichment of metallic carbon nanotubes by electric field-assisted chemical vapor deposition Original Research Article

We report herein a rational approach to increase the proportion of metallic carbon nanotubes (CNTs) in horizontally aligned ultralong CNT arrays by electric field-assisted chemical vapor deposition. In a gas flow-directed growth mode, the buoyancy caused by temperature differences near the substrate can lift catalyst particles or CNTs from the substrate into the laminar flow so that ultralong CNT arrays with mixed metallic (m-) and semiconducting (s-) CNTs can be obtained. It was verified that the percentage of m-CNTs was about 47% for pristine CNTs. When an electric field was introduced during CNT growth, the grown CNTs were polarized and the generated electric field force assisted them into the laminar flow. The greater polarizability of m-CNTs compared to s-CNTs resulted in more m-CNTs lifted and an increased m- to s-CNT ratio in the array. Measurements of CNT electrical properties showed that the percentage of m-CNTs could reach 80% when the electric field intensity was set at 200 V/cm.